The present invention relates to land based gas turbines employing gas injection for power augmentation. Specifically, a method of designing a gas metering system is provided that allows the power augmentation system to be used with more than one diluent gas or a mixture of gasses.
Diluent injection (typically steam) into the combustors of a gas turbine can increase the unit peak load capability, particularly at high ambient temperature conditions. When a fluid other than the one that the typical system was designed for is used, however, the calculated diluent or fluid flow will be incorrect, because of fluid property differences (particularly density and viscosity) in the respective fluids. To correctly control the flow of different fluids or fluid mixtures, air and steam for example, a scheme that properly accounts for fluid property differences is required.
The conventional diluent injection method is to use a single set of fluid properties in the metering logic to calculate diluent mass flow. The calculated flow is based on the measured flow element differential pressure. If, for example, a system of this type is set up for steam injection, it can only calculate steam flow. It cannot set the proper mass flow for air injection or an air/steam mixture injection. The control logic must have the proper fluid properties reentered whenever the diluent changes.
This invention provides a method that can properly meter multiple or mixtures of diluent fluids for gas turbine combustor injection for power augmentation, without requiring reentry of fluid properties when the diluent fluid is changed, and without the use of separate flow measurement devices for each diluent.
In the exemplary embodiment of the invention, the gas turbine controller logic includes multiple fluid property sets for air and steam, along with the equations necessary to compute the properties of any mixture of air and steam. Input includes signals from the steam and air injection system to the gas turbine controller logic for fluid type and mass fraction for each diluent fluid in service. The gas turbine control logic will calculate the correct fluid properties to be used in the diluent flow rate calculation. With this arrangement, a single metering tube, control valve and differential pressure instrument set can provide the required information for proper determination and control of the diluent mass flow rate, whether the diluent be air, steam or a mixture of air and steam.
Accordingly, in its broader aspects, the present invention relates to a method of augmenting power in a gas turbine plant that includes a compressor, at least one combustor, a turbine component and an output shaft, comprising a) supplying air and water to a heat recovery boiler; b) providing a turbine controller that controls supply of air, steam or a mixture of air and steam to the combustor; c) storing data in the turbine controller including properties of air, steam and equations for determining properties of any mixture of air and steam; d) measuring a differential pressure of the air, steam or mixture of air and steam across a metering tube located upstream of the combustor; e) determining substantially instantaneously the mass flow rate of the air, steam or mixture of air and steam as a function of the differential pressure and desired power output; and f) supplying the air, steam or mixture of air and steam to the combustor at the flow rate determined in step e).
In another aspect, the invention relates to a method of augmenting power in a gas turbine plant that includes a compressor, at least one combustor, a turbine component and an output shaft, comprising a) supplying air and water to a heat recovery boiler for heat exchange with exhaust gas from the turbine component; b) providing a turbine controller that controls supply of air, steam or a mixture of air and steam to the combustor; c) storing data in the turbine controller including viscosity and density of air, steam and equations for determining properties of any mixture of air and steam; d) measuring a differential pressure of the air, steam or mixture of air and steam across a metering tube located upstream of the combustor; e) determining instantaneously the mass flow rate of the air, steam or mixture of air and steam as a function of the differential pressure and desired power output; and f) supplying the air, steam or mixture of air and steam to the combustor at the flow rate determined in step e); wherein step f) is carried out with a control valve downstream of the metering tube, the control valve operatively connected to the turbine controller.
In still another aspect, the invention relates to a land based gas turbine plant comprising a compressor, a turbine component, and a combustor between the compressor and the turbine component; a heat recovery boiler arranged to receive exhaust gas from the turbine component; means for injecting air, steam, or a mixture of air and steam into the combustor; and means for substantially instantaneously calculating mass flow rate of the air, steam or mixture of air and steam.